Time and again we have always been told - don't drive when drunk.

Drunk driving, in this case, drunk boating, took the life of an 18-year-old man Monday afternoon after he was caught in the propellers of a hired boat in Sydney Harbour.

The alleged culprit was the boat's skipper.

The victim, a Korean national, was pulled from the water under the back of the boat at Athol Bay near Mosman. He was brought to Royal North Shore Hospital, where he died of injuries to his abdomen and legs.

Initial investigation showed the young Korean was aboard the 40-foot cruiser partying with some 14 other friends, aged 18 to mid-20s. He and two other friends later went off for a swim.

Seeing the swimmers were drifting away from the boat, the skipper manoeuvred the boat toward them. It was then the accident occurred, with the Korean teen trapped by the boat's propeller.

Police conducted a blood sample and other tests on everyone, including the skipper. He tested positive for alcohol.

Authorities are coordinating with the South Korean Consulate to contact the 18-year-old's relatives regarding his remains.

Police will further conduct forensic testing on the boat.